Thermal Stress Development Research Articles

Effective Young’s modulus of highly porous 3D printed mono-material and coaxial structures

The dynamic elastic response of 3D macroporous scaffolds is crucial to determine their performance under operating conditions. In this work, the elastic behaviour of 3D printed bar-shaped scaffolds of γ-Al2O3 and γ-Al2O3/graphene nanoplatelets (GNP) composites (18 vol%), fabricated by Direct Ink Writing (DIW), is investigated. Dynamic Young’s modulus (E) is studied by the Impulse Excitation Technique (IET) and compared with theoretical results obtained by Finite Element Methods (FEM) and the multi-scale material simulator GeoDict®. In addition, Resonant Ultrasound Spectroscopy (RUS) is used to characterize E of single- and bi-material coaxial struts. While additions of GNP to γ-Al2O3 lead to an increase in E, it decreases in the coaxial struts due to the development of thermal residual stresses at the core/shell interface. The suitability of combining experimental and theoretical methods for the analysis of the elastic properties and the anisotropy associated with the lattice pattern is demonstrated.

Functionally graded bi-material interface for Porcelain Veneered Zirconia dental crowns: A study using viscoelastic finite element analysis

ObjectivesDuring the manufacturing of Porcelain Veneered Zirconia (PVZ) dental crowns, the veneer-core system undergoes high-temperature firing cycles and gets fused together which is then, under a controlled setting, cooled down to room temperature. During this cooling process, the mismatch in thermal properties between zirconia and porcelain leads to the development of transient and residual thermal stresses within the crown. These thermal stresses are inherent to the PVZ dental crown systems and render the crown structure weak, acting as a precursor to veneer chipping, fracture, and delamination. In this study, the introduction of an intermediate functionally graded material (FGM) layer at the bi-material interface is investigated as a potentially viable alternative for providing a smoother transition of properties between zirconia and porcelain in a PVZ crown system. MethodsAnatomically correct 3D crown models were developed for this study, with and without the FGM layer modeled at the bi-material interface. A viscoelastic finite element model was developed and validated for an anatomically correct bilayer PVZ crown system which was then used for predicting residual and transient stresses in the bilayer PVZ crown. Subsequently, the viscoelastic finite element model was further extended for the analysis of graded sublayers within the FGM layer, and this extended model was used for predicting the residual and transient stresses in the functionally graded PVZ crown, with an FGM layer at the bi-material interface. ResultsThe study showed that the introduction of an FGM layer at the bi-material interface has the potential to reduce the effects from transient and residual stresses within the PVZ crown system relative to a bilayer PVZ crown structure. Furthermore, the study revealed that the FGM layer causes stress redistribution to alleviate the stress concentration at the interfacial surface between porcelain and zirconia which can potentially enhance the durability of the PVZ crowns towards interfacial debonding or fracture. SignificanceThus, the use of an FGM layer at the bi-material interface shows a good prospect for enhancing the longevity of the PVZ dental crown restorations by alleviating the abrupt thermal property difference and relaxing thermal stresses.

Thermo-structural analysis of a dump nozzle for conducting hot liquid sodium

Liquid sodium is found to be an essential element in nuclear reactors for transferring enormous amount of heat between source and sink. Conducting hot liquid sodium through metal pipes is witnessed to be challenging owing to the huge thermomechanical stress involved during the process. The present research work aims at designing a dump nozzle for the safe transfer of hot liquid sodium (at 923 K) to a storage tank through SS316LN pipe. Numerically simulated results showed the development of huge thermal stress at the weld junction formed between pipes and storage tank, which is primarily due to the sudden increase in temperature. The newly proposed dump nozzle with reducer/baffle (connecting pipe with storage tank) is witnessed in reducing the sudden increase in temperature and henceforth, minimized the stress intensity of the weldment by 70 %. The fatigue-creep interaction diagrams are plotted for the weld and the reducer; the results showed that the induced stress values for the parts are well below the safety envelops for the given boundary conditions of liquid sodium flow velocity and temperature. The proposed dump nozzle design is hence validated for the safe handling of transferring liquid sodium to storage tank.

Thermomagnetic responses of a thermoelastic medium containing a spherical hole exposed to a timed laser pulse heat source

The current work aims to investigate the interaction between thermal, magnetic, and elastic phenomena in a homogeneous and unbounded material that includes a spherical cavity. A laser beam with a Gaussian distribution was used to expose the solid thermal medium, thereby bringing a source of heat into the system. The study is grounded in the expanded theory of thermoelasticity without energy dissipation, which considers the interconnection between thermal, elastic, and magnetic phenomena. This theoretical framework serves as a basis for understanding the interactions and behaviors of thermal and mechanical processes within an elastic material. The system was analyzed using a direct approach, employing the Laplace transformation method to provide solutions for the system's equations. This methodology enables the computation and presentation of precise equations for several domains of concern, such as displacement, temperature, and thermal stresses. The discussion and analysis focused on a copper-based material, and graphical representations were used to demonstrate the behavior of the researched physical fields. These graphical representations aid in comprehending the development of displacement, temperature, and thermal stresses within the material caused by the laser beam and the interplay between thermal, magnetic, and elastic processes. The results demonstrate that the laser pulse parameters have a significant impact on the temperature and thermal stress distribution, thereby influencing the thermo-mechanical reactions of the solid medium. Ultimately, this study enhances our comprehension of the intricate behavior and interplay of thermal, magnetic, and elastic phenomena in thermoelastic materials.

SEM-Guided Finite Element Simulation of Thermal Stresses in Multilayered Suspension Plasma-Sprayed TBCs

This study presents novel insights into thermal stress development and crack propagation mechanisms in single- and multilayered suspension plasma-sprayed (SPS) coatings of gadolinium zirconate (GZ) and yttria-stabilized zirconia (YSZ), thermally treated at 1150 °C. By combining image processing with finite element simulation, we pinpointed sites of high-stress concentration in the coatings, leading to specific cracking patterns. Our findings reveal a dynamic shift in the location of stress concentration from intercolumnar gaps to pores near the top coat/thermally grown oxide (TGO) interface with TGO thickening at elevated temperatures, promoting horizontal crack development across the ceramic layers. Significantly, the interface between the ceramic layer and TGO was found to be a critical area, experiencing the highest levels of both normal and shear stresses. These stresses influence failure modes: in double-layer SPS structures, relatively higher shear stresses can result in mode II failure, while in single-layer systems, the predominant normal stresses tend to cause mode I failure. Understanding stress behavior and failure mechanisms is essential for enhancing the durability of thermal barrier coatings (TBCs) in high-temperature applications. Therefore, by controlling the interfaces’ roughness along with improving interfacial toughness, the initiation and propagation of cracks can be delayed along these interfaces. Moreover, efforts to optimize the level of microstructural discontinuities, such as intercolumnar gaps and pores, within the creaming layer and close to the TGO interface should be undertaken to reduce crack formation in the TBC system.

Thermal Modeling of Photovoltaic Panel for Cell Temperature and Power Output Predictions under Outdoor Climatic Conditions of Jodhpur

The rise in the temperature severely affects photovoltaic cell efficiency and hence its power output. Moreover, it also causes the development of thermal stresses that may reduce their life span. Thus, there is a need for an accurate estimation of the cell’s working temperature. In this paper, a detailed thermal model based on various heat transfer modes involved and their governing equations has been presented to estimate the cell temperature of a PV module using MATLAB software under different climatic and solar insolation conditions. In order to validate the presented model, an experimental setup has been built and operated under actual outdoor conditions of Jodhpur, a city in the Thar Desert of Rajasthan. For the peak summer month of June, the predicted glass cover outer surface temperature has been found to be within 0.2–4.5°C of experimentally measured values and the back sheet temperature is found to be within 0.5–5.5°C. The predicted and measured power outputs have been found to be within 0.85–1.2 W while the efficiency values are within 0.17–0.38%. For the early summer month of April, the variations are 0.13–4.1°C, 0.2–4.1°C, 0.44–1.65 W, and 0.1–0.5% for glass cover temperature, back sheet temperature, power output, and efficiency, respectively. Thus, the predictions of the developed thermal model have exhibited a good agreement with the experimental results. The maximum glass cover temperatures recorded were 60°C and 65.5°C when the ambient temperatures were 35°C and 42°C near the noon for the early summer and peak summer day experiments, respectively. The presented model can be used to generate a year-round cell temperature data for the known environmental data of a location, which can help in the selection or development of appropriate cooling technology at the planning stage of the installation of a solar PV plant.

A Computational Study of Solid Si Target Dynamics under ns Pulsed Laser Irradiation from Elastic to Melting Regime

The dynamic behavior of solid Si targets irradiated by nanosecond laser pulses is computationally studied with transient, thermοmechanical three-dimensional finite element method simulations. The dynamic phase changes of the target and the generation and propagation of surface acoustic waves around the laser focal spot are provided by a finite element model of a very fine uniformly structured mesh, able to provide high-resolution results in short and long spatiotemporal scales. The dynamic changes in the Si material properties until the melting regime are considered, and the simulation results provide a detailed description of the irradiated area response, accompanied by the dynamics of the generation and propagation of ultrasonic waves. The new findings indicate that, due to the low thermal expansion coefficient and the high penetration depth of Si, the amplitude of the generated SAW is small, and the time and distance needed for the ultrasound to be generated is higher compared to dense metals. Additionally, in the melting regime, the development of high nonlinear thermal stresses leads to the generation and formation of an irregular ultrasound. Understanding the interaction between nanosecond lasers and Si is pivotal for advancing a wide range of technologies related to material processing and characterization.

A comprehensive analysis of electric, thermal, and structural effects of lightning strikes on CFRP composites and protective strategies

This study examines the influence of lightning strike protection (LSP) systems and lightning parameters on thermal damage and mechanical response behavior of carbon fiber-reinforced polymer (CFRP) composites. A coupled electric-thermal-structural model in COMSOL is employed to analyze the evolution of coupled electrical, thermal, and stress distribution in CFRP composites with two types of LSP systems: copper mesh (CM) and graphene-fuzzy fiber (GF). Although CM system can effectively mitigate matrix decomposition, its high density poses a drawback. Conversely, incorporating a GF layer in CFRP reduces the area and thickness of thermal damage, accompanied by minimal stress in the underlying composite. To further enhance the mitigation of thermal damage and stress, an insulated layer is integrated between the LSP layer and the composite (CM/E/CFRP and GF/E/CFRP). The study also explores how lightning parameters influence the progression of thermal damage and stress development in CFRP and GF/E/CFRP composites. By shedding light on the crucial factors governing CFRP damage, we propose novel carbon-based tailored LSP materials that are lightweight and offer high performance to effectively protect the underlying composite from lightning strikes.

Liquid metal embrittlement in Zn-coated steel resistance spot welding: Critical electrode-contact and nugget growth for stress development and cracking

Liquid metal embrittlement (LME) crack is a severe defect which can affect the joint integrity of Zn-coated advanced high-strength steel resistance spot welds (RSW). The tensile stress that causes LME cracking is a consequence of thermal contact at the electrode-sheet interface during welding. Currently, there is no systematic study to identify the critical stages of LME occurrence during welding with understanding the tensile stress development. This research aims to address this gap by combining in-situ observation, ex-situ verification, and finite element modeling to identify the critical stages in LME cracking. The study reveals that the large LME cracks form only after a critical welding time (tcrit) of 250 ms, when the growth of the weld nugget exceeds that of the electrode-sheet contact and electrode tip-face diameter. As tcrit was attained, the LME responsible thermal gradient increased from 2000 °C/mm to 4000 °C/mm, consequently tensile stress increased from 200 MPa to 300 MPa, resulting in large LME crack. A mechanistic model explaining the effect of nugget growth rate and electrode-contact growth on thermal gradient, stress development and LME cracking was then proposed and verified through cross-comparison of crack observations. This research provides valuable insights into the critical stages of LME cracking during RSW of Zn-coated steel and suggests enhancing the growth rate of electrode-contact as a solution to mitigate this issue without altering the nugget growth rate.

Evaluation of thermal cracking probability for asphalt concretes with high percentage of RAP

The paper presents determination of the probability of thermal cracking of asphalt mixtures with different reclaimed asphalt pavement (RAP) content on the basis of laboratory tests and analytical evaluation using thermal stress development method. Probability was evaluated taking into consideration: the type and gradation of the mixture and the quality and content of RAP. Thermal stresses were determined using two models: elastic and viscoelastic. Addition of RAP decreases the low-temperature properties of all the tested asphalt mixtures. In the case of wearing and binder courses, addition of 20% of RAP increases the cracking temperature by around 5–6 °C.

Numerical investigation on the temperature uniformity of micro-pin-fin heat sinks with variable density arrangement

Temperature non-uniformity on chips has drawn the attention of researchers due to unwanted thermal stress development on chips resulting in a reduction in their life cycle and performance. In the present investigation, the heat transfer and flow characteristics of the coolant in the micro-pin-fin heat sink with variable density arrangement have been conducted numerically. The dimensions of the micro-pin-fin heat sink are 18.0 mm × 19.0 mm × 4.0 mm, and the height of the micro-pin-fin is 2 mm. Circular micro-pin-fin with diameters of 400, 500, and 600 μm, respectively have been considered. The power supply is 50 W with a heat source area of 10.0 mm × 10.0 mm. Water was the working fluid used while aluminum was used for the solid part of the heat sink. The operating pressure drop between the inlet and the outlet of the heat sink is fixed at 1500 Pa, 3000 Pa, and 5000 Pa. Ansys-Fluent was employed for the analysis. The results indicate that the temperature uniformity on the heat source for heat sink with variable density arrangement is better than that with staggered arrangement for about the same number of micro-pin-fins. The best effective thermal resistance is noted as 0.258 K/W among the heat sinks with all the configurations. In addition, the temperature difference per unit length on the heat source for heat sink with convergent arrangement at the pressure difference of 5000Pa and micro-pin-fin diameter of 600 μm was 1.34 K/mm, which is lower than the previously reported literature.

Temperature uniformity characteristics of array jet impingement cooling with the maximum cross-flow scheme

Temperature uniformity of the impingement cooling is commonly needed in many fields in order to enhance performance, reliability, and to ensure material quality. In particular, operating life of the hot components in gas turbine depends heavily on how uniformly they are being cooled to mitigate the development of thermal stresses. However, there are rather limited literatures addressing these, and the cooling uniformities of jet impingement in extreme conditions, such as the cooling of turbine vane and combustor liner, are seldom discussed. This study focused on the temperature uniformity of array jet impingement cooling with the maximum crossflow scheme, where the detailed distribution of the nonuniformly cooled areas on the target wall, as well as their correlations with the impinging flow field, and the effects of typical geometrical and fluid parameters on the uniformity were investigated. Results indicated that the arising of the high temperature zones and inverse temperature gradient pairs around them, essentially induced by the entrainment vortex and counter rotating vortex pair in the streamwise and spanwise directions respectively, are the sources of temperature nonuniformities over the impingement target surface. Moreover, increasing the impingement Reynolds number or shortening the jet-to-target spacing for higher jet Reynolds numbers could improve the temperature uniformity.

Development of a new modified TSRST test to measure the thermal stress of asphalt supporting layer in the slab track system

The unique thermal stress environment of asphalt supporting layer (ASL) in the slab track system is critical to its service safety. The extra thermal load is responsible for causing large thermal stress in ASL. A new modified thermal stress restrained specimen test (TSRST) method was developed to measure the thermal stress development of ASL during the cooling process. The high density polyethylene (HDPE) blocks were assembled onto the asphalt mixture beam to provide extra thermal load automatically during the cooling process, the modified TSRST test were conducted on two types of asphalt mixture types comparing to the standard TSRST test. The tests results show that the extra thermal load accelerates the development of thermal stress in asphalt concrete and elevates the fracture temperature and transition temperature. The modified TSRST test was proved to characterize the effect of the extra thermal load effectively, and the test results have good repeatability.

Temperature effect on elastic and fracture behaviour of lead-free piezoceramic BaTiO3

Ferroelectric ceramics, especially piezoceramics, are widely used in the field of sensors, micromanipulators, and capacitors. Barium titanate and its derivates are the first choices between lead-free materials. The main aim of the paper is to clarify fundamental processes taking place in the vicinity of Curie temperature with a focus on the fracture behaviour of pure polycrystalline barium titanate. The explanation of observed changes in the mechanical behaviour of this material is based on the experimental approach supported by numerical simulations utilising features of the real microstructure on the grain level. Several model materials with various grain microstructures were manufactured from the submicron barium titanate powder sintered at various temperatures. Two resulting materials with a suitable distribution of grains were selected for further investigation. The grain size influenced not only the exact position of the temperature of the Curie point but also the kinetics of the lattice transformation, elastic, and fracture properties. The significant drop observed in the fracture resistance was attributed to the development of localised internal thermal stresses, which was supported by the results of the performed numerical simulations. The coincidence of the volume change of neighbouring grains due to lattice transformation together with a significant variation in elastic properties can lead up to a 20% decrease in the measured fracture toughness. Understanding this behaviour is essential for the processing and correct application of lead-free barium titanate materials.

Thermal shock behavior of ZrB2-MoSi2-SiCw composites

Effect of SiCw volume fraction on thermal shock resistance (TSR) of ZrB2-20 MoSi2 composite has been studied in the present work. Three composites namely ZMSw0 (ZrB2-20 MoSi2-0 SiCw), ZMSw5 (ZrB2-20 MoSi2 - 5SiCw) and ZMSw20 (ZrB2-20 MoSi2-20 SiCw) were prepared by multi-stage spark plasma sintering at 1700 °C. TSR was measured using indentation quench technique. Results indicate that an increase in silicon carbide percentage decrease the crack growth rate and increase the critical temperature differential ΔTc, which in turn continuously raises the TSR of the composites. Development of thermal residual stresses due to thermal shock leads to excellent crack shielding and higher TSR of the ZMSw20 composite. The reduction in hardness and fracture toughness due to thermal shock for the ZMSw20 composite is lesser than that of both the ZMSw0 and ZMSw5 composites.

Design of Solar Cell Temperature-Based Single Parameter Model of PV Modules

Single parameter models are useful for assessing the impact of a particular parameter on a complex phenomenon, while holding other influencing factors at standardized constant values. Such models are essential for performance estimation and prediction of output with due parametric analysis. The output power and the efficiency of photovoltaic cells are primarily governed by cell temperature that ranges between 50°C to 75°C in different seasons in India. The increase in temperature causes the development of thermal stresses in the panel and affects its life span. This paper proposes a methodology for designing a single parameter model of a PV module with respect to cell temperature for estimating the loss of performance and accurate prediction of the power output. The proposed methodology has been validated for three different modules used by researchers. The model accuracy has been found to be better than 98% in all cases.

Numerical analysis of thermal cracking estimation of mass concrete with GGBS at an early age

At an early age, the temperature rise in mass concrete is attributable primarily to the propagation of heat due to an exothermic reaction of cementitious materials and water. The temperature variation in the mass concrete between the core and its surfaces results in the development of thermal stresses. It might occur cracking if these stresses surpass the gained tensile strength of concrete. The paper compares experimental and numerical outcomes of heat generation in concrete mould 0.15 m × 0.15 m × 0.15 m in size. Four concrete mixtures with ground granulated blast-furnace slag (GGBS) replacement to cement 0%, 10%, 30%, and 50% were used in the study. Virtual Cement and Concrete Testing Laboratory (VCCTL) software was used for obtaining the degree of hydration and adiabatic temperature of the four mixtures. Finite element modeling of these mixtures observed good agreement with experimental testing captured by the thermometer. Following that, numerical simulation was utilized to study the effect of the block size (cubic models with edge length 0.5 m, 1.0 m, 2.0 m, and 3.0 m) on temperature rise and the associated risk of cracking in mass concrete blocks.

Thermal stress analysis of disc brake using analytical and numerical methods

This article presents study of the thermal stress development in brake disc and the associated life cycle of the disc. The thermal stress analysis of disc brake under the first brake application and the influences of thermal loads on stress development of the disc have been investigated. The temperature distribution was conducted as a function of disc thickness and braking time. The study was done on the disc brake of Sports Utility Vehicle with a model of DD6470C. Partial solution approach was used to solve analytical temperature distribution through the thickness. The model was done using representative areas of the disc exposed to high temperature whose distribution result was obtained as a function of disc thickness and braking time. The solutions of coupled thermal transient fields and stress fields were obtained based on thermal-structural coupled analysis. Based on the model developed for the study, the positions of high and low stress formations were investigated, and it has been observed that thermal stress and temperature gradient show similar behavior through the thickness of disc. Generally, high temperature and stress components were found on the rubbing surfaces of the disc.

On miniaturisation of spirally wound tubular heat exchanger

Spirally coiled multilayer, Giauque-Hampson type heat exchangers, the classical examples of early generation cryogenic heat transfer devices, are best known for their unique and favourable features. These exchangers are capable of handling multiple fluid streams in different phases in a single unit, typically meant for high Ntu applications, operational over a wide range of temperature and pressure with minimum thermal stress development. On the negative part, they belong to the non-compact class of heat exchangers. As the trend of miniaturisation is gradually diffusing into almost every engineering discipline, the development of a compact system is the call of the present era. While probing the prospect of miniaturising multilayer spirally wound tubular (Giauque-Hampson) heat exchangers satisfying the compactness criteria, this article presents the design, fabrication, and testing of a miniature, compact, laboratory-scale prototype. Initially, the pros and cons of miniaturisation have been studied based on the ‘goodness factors’. Subsequently, a step-by-step methodology is proposed to design a compact and miniature heat exchanger geometry, subjected to design constraints. Description of critical fabrication steps is followed by the experimental performance evaluation of the prototype. The heat exchanger effectiveness is calculated based on the steady-state experimental data. Performance degradation is linked to the prevailing non-ideal operating conditions causing external heat ingress. The analysis including heat leak shows good agreement between the experimental results and theoretical predictions.

Chemical reactions and thermal stress induced microstructure evolution in 2D-Cf/ZrB2-SiC composites

Fibers degradation and matrix cracks are very common during fabrication of composites, which seriously reduces the reliability and properties of the composites. In this work, 2D-Cf/ZrB2-SiC composites were fabricated by a joint processing of slurry infiltration and hot pressing. Based on thermal kinetics calculation, finite element simulation and detailed microstructure characterization, fibers degradation and matrix cracks formation mechanisms of the composites are discussed and revealed. Oxide impurities including SiO2 and ZrO2 react with carbon fibers, resulting in formation of ZrC, SiC particles and etching pits on the fibers, which also leads to a strong bonding between the fibers and matrix. On the other hand, thermal expansion mismatch between the fibers and matrix gives rise to serious thermal stress in the composites. The thermal stress distribution and development are analyzed by finite element simulation, which is in good agreement with the cracks’ formation in the composites. Based on the revealed microstructure evolution mechanisms, a potential solution to mitigate fibers degradation and matrix cracks is put forward.